Scroll type compressors with one orbiting scroll and one fixed or stationary scroll are well known. The Scrolls in these compressors have parallel end plates and involute spiral wrap elements of like pitch. The wrap of one scroll makes line contacts with the wrap of the other scroll and axial edges of the wraps include seals which contact the adjacent scroll end plate to define fluid pockets. As the orbital scroll orbits relative to the fixed scroll, the locations of the contact lines move along the surfaces of the wraps toward the center of the scrolls, the pockets decrease in size compressing the fluid contained in the pockets and the fluid is moved toward the center of the scrolls. A scroll discharge aperture is provided near the center of the fixed scroll to allow compressed fluid to pass from the scrolls into an exhaust or discharge cavity. The exhaust cavity is connected to a fluid discharge opening in the compressor housing.
The compressed fluid in the scroll pockets exerts a force on the scroll end plates which tends to separate the scrolls. An axial thrust assembly is employed to limit axial separation of the scrolls and thereby maintain sealing between the scroll end plates and the axial edges of the wraps. Compressor efficiency drops if fluid moves between the axial edges of the wraps and the end plates, to pockets at a lower pressure. Axial thrust assemblies including a plurality of balls in a space between facing surfaces on the compressor housing and the orbital scroll are in common use to limit axial movement of the orbital scroll and thereby maintain sealing.
An anti-rotation assembly is provided to prevent rotation of the orbital scroll. The assembly may include a first ring with a series of apertures that each surround one of the axial thrust balls and a second ring with apertures that also receive the axial thrust balls. The first ring is fixed to the compressor housing. The second ring is fixed to the orbital scroll. The apertures in the two rings have diameters which will permit orbital movement of the balls and the orbital scroll and prevent rotation of the orbital scroll.
The compressor drive includes a crankshaft rotatably journaled in the compressor housing. An eccentric bushing is journaled on the crankshaft crank pin. The eccentric bushing is also received in a bore in a boss on the forward wall of the orbital scroll end plate. A bearing is provided in the bore in the boss to allow free rotation of the eccentric bushing relative to the orbital scroll.
The eccentric bushing is retained on the crankshaft crank pin by a clip or snap ring. The snap ring limits axial movement of the eccentric bushing on the crankshaft crank pin. Limits on axial movement of the eccentric bushing are required to insure that a balance weight attached to the eccentric bushing does not contact the end plate of the orbital scroll and to insure that the eccentric bushing does not contact the end plate of the orbital scroll.
Snap rings can be difficult to install. Occasionally they are not properly seated in a machined groove in the crankshaft crank pin and fall off after assembly. The loose snap ring may damage the bearing which rotatably receives the eccentric bushing in the bore in the orbital scroll. The eccentric bushing , which is not retained on the crank pin, can move axially along the crank pin until the balance weight contacts the orbital scroll or the eccentric bushing contacts the orbital scroll end plate.